1. Technical Field
The present disclosure generally relates to a method and associated instrumentation for implant insertion and, in particular, to a method and instrumentation for insertion of spinal implants to facilitate fusion of adjacent vertebral bodies.
2. Background of the Related Art
A large number of orthopedic procedures involve the insertion of either natural or prosthetic implants into bone or associated tissues. These procedures include, for example, ligament repair, joint repair or replacement, non-union fractures, facial reconstruction, spinal stabilization and spinal fusion. In a typical procedure, an insert, dowel or screw is inserted into a prepared bore formed in the bone or tissues to facilitate repair and healing. Some implants are particularly configured with cavities and bores to facilitate bony in-growth and enhance anchoring of the implant at the insertion site. Implants in the form of fusion cages having internal cavities to receive bone growth stimulation materials such as bone chips and fragments are disclosed, for example, in U.S. Pat. No. 4,501,269 to Bagby; and U.S. Pat. No. 4,961,740 to Ray et al. These types of implants are particularly well suited for intervertebral spinal fusion procedures necessitated by injury, disease or some degenerative disorder of the spinal disc. Subsequently, there may be progressive degeneration leading to mechanical instability between adjacent vertebrae necessitating direct fusion of the vertebrae while maintaining a pre-defined intervertebral space. This fusion may be accomplished by the insertion of one or more of the specialized implants as discussed above and also discussed in commonly assigned U.S. Pat. No. 5,026,373, the contents of which are incorporated herein by reference.
Both anterior (transabdorninal) and posterior surgical approaches are used for interbody fusions of the lumbar spine. Fusions in the cervical area of the spine are primarily performed using a posterior approach. Typically, an implant such as a plug, dowel, prosthesis or cage is inserted into a preformed cavity inside the interbody, interdiscal space. Since it is desirable in these procedures to promote a “bone to bone” bridge, connective tissue and at least a portion of the distal tissue is removed. Preferably, relatively deep cuts are made in the adjacent bones in order to penetrate into the softer, more vascularized cancellous region to facilitate bone growth across the implant.
One of the more critical tasks performed in the insertion of a surgical fusion implant, particularly, in intervertebral spinal fusion, is the formation of the implant receiving cavity or bore between/within the adjacent vertebrae. More particularly, the drilled bore must be equally centered within the intervertebral space and preferably parallel to the vertebral end plates to ensure removal of equal portions of bone from the adjacent vertebrae throughout the length of the cut and subsequent appropriate seating of the implant relative to the vertebral bodies. In addition, the length of the cut by the drill must be accurate depending upon the particular surgical needs for the patient and/or the length of the implant to be inserted.
Surgical instruments for spinal fusion implant insertion are known. Among several instruments, for example, U.S. Pat. No. 6,083,225 to Winslow et al., the contents of which are incorporated herein by reference, discloses an improved type of instrumentation and method for providing optimal alignment for the drilling, tapping and reception of spinal implant. This method uses a particular surgical retractor for inserting into the intervertebral space to distract adjacent vertebrae and performing the surgical procedure with instrumentation inserted through an opening of the surgical retractor.